Conventionally, polarizing plastic lenses that block light that is polarized in a specific direction, such as light reflecting off the surface of water, are known (for example, see the following documents, the contents of which are expressly incorporated herein by reference in their entirety).    Document 1: Japanese Unexamined Patent Publication (KOKAI) No. 2007-316595 or English language family member US2009/091825A1    Document 2: Japanese Translated PCT Patent Application Publication (TOKUHYO) No. 2007-523768 or English language family members US2007/098999A1 and U.S. Pat. No. 7,767,304.
The polarizing lenses described in Documents 1 and 2 are polarizing lenses that are manufactured by embedding a polarizing film within the lens and casting a curable composition around the polarizing film, which is then cured by heating (also referred to hereinafter as the cast polymerization method or casting method).
In the polarizing lens prepared by the manufacturing method set forth above, astigmatism is sometimes produced by deformation of the lens. That is because heating during the manufacturing process deforms the polarizing film embedded within the lens. Due to this deformation, the shape of the lens surface changes. Eyeglass wearers who observe an object through an eyeglass lens that has developed astigmatism sense wear discomfort (blurring and the like) due to the astigmatism. Thus, the astigmatism should be prevented or reduced in order to provide an eyeglass lens affording a good wearing sensation.
An aspect of the present invention provides for a means for obtaining a polarizing lens with little astigmatism by inhibiting deformation of the polarizing lens within which the polarizing film is embedded.
An aspect of the present invention relates to a method of manufacturing a polarizing lens, which comprises:
conducting curved surface processing to change a shape of a polarizing film into a shape of a curved surface;
conducting heat treatment by heating the polarizing film that has been processed into a curved surface to a heating temperature of equal to or higher than 105° C. but less than 150° C.;
assembling an upper mold, a lower mold, and a seal member to provide a casting mold having a cavity within which the polarizing film following the heating treatment is positioned, the upper mold and the lower mold being positioned opposite each other so as to sandwich the polarizing film at a space therebetween, and the seal member sealing the space between the upper mold and the lower mold;
casting a curable composition into the cavity;
curing the curable composition to provide a polarizing lens within which a polarizing film is positioned; and
separating the polarizing lens thus provided from the casting mold.
Documents 1 and 2 above disclose that the polarizing film is processed into a curved surface before positioning the polarizing film within the casting mold to obtain a polarizing lens within which a polarizing film is embedded. In Document 1, it is disclosed that the polarizing film is heated to process it into a curved surface. In Document 2, it is disclosed that the polarizing film is dried at a prescribed temperature. However, in these documents, there is no disclosure that the polarizing film should be heated following processing into a curved surface.
By contrast, in the above manufacturing method, the polarizing film following curved surface processing is heated to a heating temperature of equal to or higher than 105° C. but less than 150° C. before being positioned within the casting mold. Such heating can predeform (shrink) the polarizing film that has been curved surface processed prior to positioning it within the casting mold. It is presumed that, during subsequent processing, shrinkage that would deform the surface shape of the lens is either not induced or the degree of shrinkage is small. The present inventors presume that this is why the above manufacturing method can provide a polarizing lens with little astigmatism. In the present invention, the “upper mold” refers to a mold having a molding surface for molding the object-side surface of the eyeglass lens. Normally, the molding surface is a concave surface for forming a convex surface. The “lower mold” is a mold having a molding surface for forming the eyeball-side surface of the eyeglass lens. Normally, the molding surface is a convex surface for molding a concave surface. The “object-side surface” of the lens means the surface constituting the lens that is on the side of the object that is visually recognized when the lens is worn as an eyeglass. The “eyeball-side surface” of the lens means that surface constituting the lens that is on the side of the eyeball of the wearer when the lens is worn as an eyeglass.
In an embodiment, the above manufacturing method comprises moistening the polarizing film prior to the curved surface processing.
In an embodiment, in the above manufacturing method, the polarizing film prior to curved surface processing is moistened while being heated, cooled, and then curved surface processed.
In an embodiment, the above cooling is conducted by placing the moistened polarizing film at room temperature.
In an embodiment, the above manufacturing method comprises positioning the polarizing film in the above assembling of the casting mold such that the minimum distance between the inner surface on the cavity side of the upper mold and the polarizing film is equal to or more than 0.3 mm and equal to or less than 0.7 mm.
The polarizing lens prepared by using the casting mold assembled as set forth above comprises:
a first lens substrate having an object-side surface;
a second lens substrate having an eyeball-side surface; and
a polarizing film, positioned between the first lens substrate and the second lens substrate, such that a minimum distance between the polarizing film and the object-side surface is equal to or more than 0.3 ram and equal to or less than 0.7 mm.
The polarizing lens with the above structure is useful as a semifinished lens. This point will be described in greater detail below.
Eyeglass lenses are normally roughly classified into finished lenses and semifinished lenses. A finished lens means a lens in which the refractive surface (normally, a convex surface) on the object side of the lens and the refractive surface (normally, a concave surface) on the eyeball side are both mirror-finished optical surfaces that satisfy the prescription lens power, and in which there is no need for the curved surface processing of an optical surface. Finished lenses include lenses that have been subjected to edging, and lenses that have not yet been subjected to edging.
A semifinished lens (also referred to as a “semi-lens”, hereinafter) has a meniscus shape in which one of the surfaces is normally convex and the other surface is of a concave, but without a vision-correcting function. Just the convex surface of the lens is an optical surface that has been processed to a mirror surface; the concave surface is an unprocessed surface. The design of the lens thickness leaves a machining allowance for removal by processing so that the lens manufacturer, in response to the lens prescription power, can process (including grinding, curve-generating, and polishing) the surface on the concave side to finish a lens with a vision-correcting function. In the present invention, the above-described finished and semifinished lenses are defined as eyeglass lenses. That is, eyeglass lenses include finished lenses, which are lenses having a vision-correcting function that optically satisfies a prescription power, as well as semifinished lenses, which are processed into lenses having a vision-correcting function that optically satisfies a prescription power.
When the above polarizing lens within which a polarizing film is embedded is a semifinished lens, the maximum value of the machining allowance for processing such that the polarizing film is not exposed or eliminated is determined by the distance between the polarizing film and the concave surface (the surface that is surface processed to function as the refractive eyeball-side surface). The closer the polarizing film approaches to the concave surface, the smaller the machining allowance becomes. Accordingly, the lens that is obtained following surface processing ends up being thick. Generally, the thickness of a normal finished lens that doesn't include a polarizing film is about 1.1 mm at its thinnest point. In a polarizing lens (semifinished lens) in which the minimum distance from the object-side surface is equal to or less than 0.7 mm, by envisioning surface processing to the processing limit, an eyeglass lens in which the thickness at the thinnest spot is about 1.1 mm can be provided by surface processing the concave surface. Additionally, if the minimum distance between the object-side surface and the polarizing film is made equal to or more than 0.3 mm, the forming of the eyeball-side surface is facilitated during manufacturing.
As set forth above, a polarizing lens comprising a first lens substrate having an object-side surface; a second lens substrate having an eyeball-side surface; and a polarizing film, positioned between the first lens substrate and the second lens substrate, such that the minimum distance between it and the object-side surface is equal to or more than 0.3 mm and equal to or less than 0.7 mm, is useful as a semifinished lens for obtaining a polarizing lens (finished lens) comprising a polarizing film within the lens.
In an embodiment, the above manufacturing method comprises, in the assembly of the above casting mold, adhering with an adhesive the perimeter portion of the inner surface on the cavity side of the upper mold and the perimeter portion of the polarizing film at two or more points.
This point will be described in greater detail.
In the manufacturing by the cast polymerization method of a polarizing lens in which a polarizing film is embedded, in the methods described in above Documents 1 and 2, a gasket is employed as a material for sealing off the cavity of the casting mold and a mounting part provided on the gasket is used to position the polarizing film. However, in such methods, irrespective of the thickness and shape difference (curved surface precision) of the polarizing film, the holding position of the polarizing film ends up being determined by the gasket design and manufacturing precision. As a result, the position of the polarizing film following molding ends up fluctuating. Thus, it becomes necessary to mold the lens to a thickness that takes this fluctuation into account. The lens ends up being thicker than an ordinary eyeglass lens (an eyeglass lens that doesn't include a polarizing film). By contrast, based on the method of adhering the upper mold to the polarizing film with the adhesive, based on the amount of adhesive applied (the height of the adhesive column), the distance between the inner surface of the upper mold and the polarizing film, that is, the distance between the polarizing film and the object-side surface of the lens that is obtained by cast polymerization, can be freely set. Thus, it becomes possible to resolve the above-described problems occurring in methods employing gaskets.
In an embodiment, the above seal member is a tape having an adhesive layer.
When a tape is employed as a material for sealing off the cavity of the casting mold, it is difficult to provide a polarizing film-positioning part such as a gasket. Thus, when manufacturing a polarizing lens by cast polymerization, a gasket is normally employed. By contrast, based on the method of adhering the upper mold and the polarizing film by means of the adhesive, it is possible to position and hold the polarizing film within the cavity of the coasting mold without using a gasket having a mounting part for positioning and holding the polarizing film. Accordingly, when manufacturing a polarizing film by cast polymerization, a tape, a simple and inexpensive material, can be employed.
In an embodiment, in the above manufacturing method, the curved surface processing is conducted by pressing down with the polarizing film positioned on the convex surface mold to transfer the convex surface shape to the polarizing film.
In an embodiment, the above heat treatment is conducted with the polarizing film positioned on the convex surface mold following the above pressing, without removing it from the convex surface mold.
In an embodiment, the heating temperature is equal to or higher than 120° C. but less than 150° C.
In an embodiment, the above manufacturing method comprises coating a heat-curable composition on the polarizing lens that has been separated from the casting mold and then conducting heating to form a cured coating.
A further aspect of the present invention relates to a polarizing lens comprising:
a first lens substrate having an object-side surface;
a second lens substrate having an eyeball-side surface; and
a polarizing film, positioned between the first lens substrate and the second lens substrate, such that the minimum distance between it and the object-side surface is equal to or more than 0.3 mm and equal to or less than 0.7 mm;
in which that the difference (Rmax−Rmin) between the maximum radius of curvature Rmax and the minimum radius of curvature Rmin at the geometric center of the object-side surface is less than 4 mm.
The above polarizing lens will be further described below.
It is already described above that the polarizing lens is desirably a semifinished lens in which the minimum distance between the object-side surface and the polarizing film is equal to or more than 0.3 mm and equal to or less than 0.7 mm. In a polarizing lens in which the polarizing film is positioned relatively close to the object-side surface in this manner, the tendency for the object-side surface to be deformed due to deformation of the polarizing film is strong. However, such deformation may cause the above-mentioned astigmatism. By contrast, based on the present invention as set forth above, it is possible to prevent the surface shape of the object-side surface from changing due to deformation of the polarizing film. The difference (Rmax−Rmin) between the maximum radius of curvature Rmax and the minimum radius of curvature Rmin at the geometric center of the object-side surface can be used as an indicator that no deformation has occurred. So long as the value thereof is less than 4 mm, the eyeglass lens can be considered to be one for which an eyeglass wearer will sense no (or few) use defects due to astigmatism. The polarizing lens according to an aspect of the present invention can be employed as an eyeglass lens producing such a good sensation when worn.
A further aspect of the present invention relates to a method of manufacturing a polarizing lens comprising:
assembling an upper mold, a lower mold, and a seal member to provide a casting mold having a cavity within which the polarizing film is disposed, the upper mold and the lower mold being positioned opposite each other so as to sandwich the polarizing film at a space therebetween, and the seal member sealing the space between the upper mold and the lower mold, with the maximum diameter of the polarizing film being the same or smaller than the maximum diameter of the inner surface on the cavity side of the upper mold, and with the perimeter portion of the inner surface on the cavity side of the upper mold being adhered by means of adhesive to the perimeter portion of the polarizing film at two or more points;
casting a curable composition into the cavity;
heat curing the curable composition to provide a polarizing lens within which a polarizing film is positioned; and
separating the polarizing lens thus provided from the casting mold.
By assembling a casting mold in this manner and casting a curable composition (also referred to hereinafter as a “lens monomer,” which can also contain various curable components such as oligomers and prepolymers in addition to monomers) into the cavity, the lens monomer surrounds the polymerizing film within the cavity on two sides, thereby permitting the smooth injection of lens monomer into the cavity.
In an embodiment, the adhesive is solidified in columnar form so as to have a certain height and support the polarizing film.
In an embodiment, the seal member is a tape having an adhesive layer.
In an embodiment of the various embodiments set forth above, the curable composition is a thiourethane or thioepoxy resin.
In an another embodiment, the adhesive is positioned in spots that are removed during mounting of the lens into an eyeglass frame.
The present invention can provide a polarizing lens within which a polarizing film is positioned, with little deformation on the object-side surface. The polarizing lens that is provided in this manner is useful as a semifinished lens.